This invention relates to rapid forming of flexible foam shells from ethylene-containing foam sheet materials. It relates particularly to an improved method and apparatus for rapidly heating and die forming ethylene-containing foam sheet to produce stable drawn shell shapes.
Conventional slow rate forming of plastic foam sheet materials such as polyethylene and polystyrene into various forms and shapes using vacuum forming procedures is known. However, a major problem encountered with rapidly thermoforming ethylene-containing foam sheet materials into desired shapes at rates exceeding about 10 cycles/minute is the flexibility and low heat conductivity of the material, and the time needed for the formed foam shapes to thermally stabilize after heating so as to maintain the desired formed shape. Because of a need for increased rates for producing such formed ethylene-containing foam shapes, it is necessary to achieve rapid forming and stabilization of the formed ethylene-containing foam shells, such as at least 10 forming cycles/minute and even up to 30 or more cycles/minute. However, the problems encountered with rapidly heating and forming ethylene-containing foam sheets into stable deep drawn foam shapes have been advantageously and unexpectedly overcome by the present invention.